28 
BULLETIN 906. "C. S. DEPAETVLEXT OE AGBICULTUEE. 
done by building a screen completely around the outlet pipe. Some 
screens are built in the form of a long narrow trough which is 
screened on all sides, the outlet being beneath the screen. Such a 
screen can be set in an open ditch that is widened out a little at the 
pipe inlet. 
Screens have also been designed that are self cleaning, reliance 
being placed on the velocity of the water to keep the screens open. 
Care should always be taken to prevent trash entering a ditch or 
pipe line where water is finally distributed through orchard hydrants 
having small openings. It is especially necessary to take proper 
Fig. 6. — Serrline basin and screens. 
precautions at the intake where the water is diverted from a flowing 
stream. For comparatively small heads of water it is sometimes 
possible to bury the first 20 or 30 feet of pipe under the stream bed 
laying the pipe with open joints and covering it with gravel. This 
will prevent all floating material entering the pipe and should keep 
out the sand. Some comparatively large mains have been protected 
at the intake in this manner. 
Open ditches bordered by shade trees are continually gathering 
leaves which are particularly harmful in clogging screens, as the 
leaves will flatten out against a fine mesh screen and may completely 
obstruct the flow of water. 
Where pipes are fed by open ditches and have sufficient grade so 
that the velocity of water will transport sand or small gravel, the 
